Developing mechanism using magnetic brush

ABSTRACT

A magnetic brush type developing mechanism in an electronic copying machine characterized by being provided with at least two developing magnetic brush rolls having different applied bias voltages.

United States Patent Handa 1 1 Dec. 23, 1975 1 DEVELOPING MECHANISM USING 3,670,700 6/1972 Britt et a1 118/637 MAGNETIC BRUSH 3,674.532 7/1972 Morse 355/3 DD 3,805,739 4/1974 Feldeiscn et a1 118/637 Inventor: Kenichi l-landa, Ebina, Japan Assignee: Fuji Xerox C0., Ltd., Tokyo, Japan Filed: May 10, 1974 Appl. N0.: 468,974

Foreign Application Priority Data May 10. 1973 Japan 48-51199 US. Cl 118/637; 427/18 lnt. Cl. G03G 15/10 Field of Search 118/637; 117/175;

References Cited UNITED STATES PATENTS 7/1971 Cheng 118/637 Primary ExaminerMervin Stein Assistant Examiner-Douglas Salser Attorney, Agent, or Firm-Gerald J. Ferguson, Jr.; Joseph J. Baker [5 7 ABSTRACT A magnetic brush type developing mechanism in an electronic copying machine characterized by being provided with at least two developing magnetic brush rolls having different applied bias voltages.

3 Claims, 2 Drawing Figures US. Patent Dec. 23, 1975 3,927,641

DEVELOPING MECHANISM USING MAGNETIC BRUSH BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a magnetic brush system developing mechanism in an electronic copying machine.

2. Description of the Prior Art In the conventional developing systems using magnetic brushes in electrophotographic copying machines, the development has been practiced by contacting a developer (prepared by mixing carrier, which is a powdery magnetic substance, and toner composed of resin capable of forming visible images) on the external surface of a sensitive drum by using magnetic brush rolls so that the toner will be deposited on the electrostatic latent images formed on the external surface of said sensitive drum. The copying machine employing this developing system, as compared with the cascade system copying, machine, has the advantages that the apparatus itself can be reduced in size and that it is made possible to obtain copies of an original having a wide image area (solid area).

As shown in FIG. 1, this magnetic brush developing system usually comprises an electric charging area A, an exposure area B, a developing area C, a transfer area D and a cleaning area E, said areas being arranged successively in that order around a sensitive drum -1. The positive charges are imparted in the charging area A, and the electrostatic latent images corresponding to the light and shade patterns of the original a are formed in the exposure area B. These electrostatic latent images are visualized in the developing area C by a magnetic brush developing device 2, with the thus visualized images being transferred in the transfer area D onto a copying paper delivered from a paper feeder mechanism b, and after completion of the transfer, the surface of the sensitive drum 1 is cleaned in the cleaning area E to get prepared for the next copying cycle. This developing device 2, as shown on an enlarged scale in FIG. 2, comprises a case 3, five pieces of magnetic brush rolls 4, 5, 6, 7 and 8, an adjusting plate 9 and a guide plate 10. In the case 3 is contained the developer d which is composed of colored powdery particles called toner and carrier particles.

Each of said magnetic brush rolls 4, 5, 6, 7 and 8 comprises a permanent magnet fixed in the inside of a cylinder having the uneven external surface, whereby said developer d is moved in the direction of arrow F in accordance with rotation of said cylinders. Of said five pieces of magnetic brush rolls 4, 5, 6, 7 and 8, four of them (5, 6, 7 and 8) which are contacted with the sensitive material 11 on the surface of the sensitive drum 1 are so-called developing magnetic brush rolls or the rolls used exclusively for developing operation, and the first roll 4 alone is used for carrying the developer d adjusted by the adjusting plate 9. The guide plate 10 acts to separate the developer d from the final magnetic brush roll 8 and return it back to the initial position.

The development is the operation for visualizing the latent images formed on the sensitive material 11 by contacting the developer d with said sensitive material 11 such that the toner in the developer d will be deposited on the image portions in the latent image section formed on said material 11 but not deposited on the background portions so as to visualize the latent images. For accomplishing such developing operation most effectively, it needs to apply to said developing magnetic brush rolls 5, 6, 7 and 8 a bias voltage (V of a value intermediate between the high potential (V,) at the latent images area and the low potential (V at the background. The value of this bias voltage gives a large influence to the image quality obtained. That is, the greater the difference (V -V between the background potential and the bias voltage of the magnetic brush rolls, the lesser the fouling of the background, while the greater the difference (V V between the potential at the image area and the bias voltage of the magnetic brush rolls, the higher the density of the image area. Thus, the fouling of the background and the image density are in a reciprocal relation. Therefore, the bias voltage of the magnetic brush rolls must be selected to provided an optimum value by considering the abovesaid two factors.

Usually, the developing capacity is proportional to the difference (V, V between the potential in the image area on the latent image section and the bias voltage of the magnetic brush rolls and also to the time for which the latent images are exposed to the developer. It is therefore one method for elevating the developing capacity to make arrangement such as to enlarge the value of difference (V V between said image area potential and the bias voltage of the developing magnetic brush rolls by enlarging the difference (V V between the image area potential and the background potential. It is however quite impossible with the presently available techniques to appreciably improve said factors owing to the counteracting properties of the sensitive material and exposure.

Therefore, in a high speed copying machine where the peripheral surface speed of the sensitive drum 1 is increased, the number of developing magnetic brush rolls is also increased correspondingly to the increase of speed, thus cancelling the original merit of the magnetic brush type developing system that the developing apparatus can be reduced in size as compared with the cascade type developing system. Further, as the number of developing magnetic brush rolls is increased, the number of spaces other than the developing areas, that is, the spaces (shown by G in FIG. 2) defined by the sensitive drum 1 and every two adjoining brush rolls, for examples rolls 5 and 6, is also increased, and the toner particles isolated from the carrier due to centrifugal force developed by rotation of the rolls or due to impingement of the developer d against the outer surface of the sensitive drum 1 get into these spaces and deposite on the background areas other than image portions on the external portion surface of the sensitive drum 1, causing soil of the background and excessively deteriorated image quality.

SUMMARY OF THE INVENTION It is therefore the primary object of the present invention to provide an improved magnetic brush type developing mechanism in which above mentioned defects are overcome. Whereby the desired reproduction BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a general schematic view of a known copying apparatus capable of applying to the present invention, and

FIG. 2 is an enlarged view of the developing mechanism in the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now, the invention is described in detail by Way of an embodiment thereof with reference to FIG. 2 of the accompanying drawings.

Above-said floating toner particles are one of the causes of fouling of the background. All of these toner particles carry electric charges, so that by differentiating the bias voltages applied to the respective developing magnetic brush rolls to provide potential differences between said respective rolls, it is possible to check the toner particles floating in each said space by the action of an electric field present between each adjoining rolls and to thereby reduce deposition of such toner particles on the external surface of the sensitive drum 1.

For instance, in FIG. 2, if a bias voltage of a value lower than the potential at the background is applied to the magnetic brush rolls 4, 6 and 8 and a bias voltage 50 to 200 V higher than the background is applied to the magnetic brush roll 5, which is the final developing roll, and to another magnetic brush roll 7, it is possible to obtain a reproduction markedly improved both in image density and in soiling of the background as compared with the conventional systems where a same bias voltage is applied to all the rolls. Also, as the bias voltage of the final developing magnetic brush roll produces the greatest influence to the foulding of the background, it is possible to obtain a similar effect by differentiating only the bias voltage of said roll 5 from that of the other rolls. In this case, the developing magnetic brush rolls other than said final roll 5 are applied with a bias voltage lower than the background potential to enlarge the difference (V V between the potential at the image section and the bias voltage to the magnetic brush rolls so as to sufficiently elevate the developing capacity at the image section while maintaining the bias voltage of said final developing roll 5 at a value sufficiently higher than the background potential, whereby the toner particles on the peripheral surface of the sensitive drum 1, in the developing area before the final magnetic brush roll 5, can be drawn to said roll 5 to thereby effect cleaning of the background, thus allowing obtainment of a high density image with little soiling of the background.

Although there has been described above and shown in FIG. 2 an arrangement where the direction of rotation of the peripheral face of the sensitive drum 1 in the developing area is opposite to the direction of rotation of the magnetic brush rolls, it is also possible, if both sensitive drum and magnetic brush rolls are rotated in the same direction, to obtain the same results as above by maintaining the bias voltage of the final developing roll higher than the background potential while keeping the bias voltage of other rolls lower than the background potential as described above Also, although in the shown embodiment four pieces of magnetic brush rolls designed for performing development and one piece of magnetic brush roll designed for performing carriage are provided, the principle of the present invention can be as well applied to any type of magnetic brush developing system where more than two developing magnetic brush rolls are provided, and such applications are all embranced within the scope of the present invention.

As described above in detail, according to the present invention, there are provided more than two developing magnetic brush rolls which are different in applied bias voltage from each other, or the bias voltage applied to the final developing magnetic brush roll is differentiated from that of the other rolls, so that movement of the toner particles floating in the spaces between the adjacent rolls can be checked by dint of the potential difference between the adjoining magnetic brush rolls to minimize deposition of such toner particles on the background other than the image areas on the external surface of the sensitive drum, thereby enabling obtainment of the reproductions with high image density and little soiling in the background.

While the present invention has been illustrated by a detailed description of a preferred embodiment thereof, it will be obvious to those skilled in the art that various changes in form and detail can be made therein without departing from the true scope of the invention.

What is claimed is:

1. In a magnetic brush type developing mechanism having at least two developing magnetic brush rolls, said developing mechanism developing a latent image on a moving recording material with magnetic toner, the improvement comprising means for applying to a first magnetic brush roll encountered by said latent image a first potential, the absolute value of which is substantially greater than the absolute value of the background potential of said latent image and means for applying to a second magnetic brush roll immediately adjacent to said first roll and encountered by said latent image prior to said first roll a second potential, the absolute value of which is less than said absolute value of the background potential whereby development of the image portion of said latent image is enhanced due to the large potential difference between the potential of said image portion and said second potential while background fogging is lessened due to the large potential difference between said first potential and said background potential which attracts the magnetic toner from the space between said first and second magnetic rolls adjacent the recording material.

2. The improvement as in claim 1 including more than two of said magnetic brush rolls and means for applying said first potential to alternate rolls including said final roll and means for applying said second potential to the remaining rolls.

3. The improvement as in claim I where said first potential is 50 to 200 volts greater in absolute magnitude than said absolute value of the background potential. 

1. In a magnetic brush type developing mechanism having at least two developing magnetic brush rolls, said developing mechanism developing a latent image on a moving recording material with magnetic toner, the improvement comprising means for applying to a first magnetic brush roll encountered by said latent image a first potential, the absolute value of which is substantially greater than the absolute value of the background potential of said latent image and means for applying to a second magnetic brush roll immediately adjacent to said first roll and encountered by said latent image prior to said first roll a second potential, the absolute value of which is less than said absolute value of the background potential whereby development of the image portion of said latent image is enhanced due to the large potential difference between the potential of said image portion and said second potential while background fogging is lessened due to the large potential difference between said first potential and said background potential which attracts the magnetic toner from the space between said first and second magnetic rolls adjacent the recording material.
 2. The improvement as in claim 1 including more than two of said magnetic brush rolls and means for applying said first potential to alternate rolls including said final roll and means for applying said second potential to the remaining rolls.
 3. The improvement as in claim 1 where said first potential is 50 to 200 volts greater in absolute magnitude than said absolute value of the background potential. 